The present invention relates to a method for assembling a plurality of concentrically disposed members such as, for example, members of a fuel injector nozzle and, more particularly, an electro-magnetic fuel injector for use in an automobile fuel supply system.
Generally, an electro-magnetic fuel injector includes a valve seat in an interior portion of a nozzle vane body fashioned as a cylindrical component, and a fuel passage, with the fuel passage being opened and closed by a valve movable toward and away from the valve seat by a linear reciprocating movement. The reciprocating movement of the movable valve is ordinarily caused by an energization of an electro-magnetic coil and a force of a return spring upon a de-energization of the coil.
For a guiding motion of the movable valve, a chip is fashioned as an inner cylindrical component in which an inner diameter portion thereof functions as a valve guiding member, the chip being disposed in the interior portion of the nozzle as described in, for example, Japanese Patent Laid-Open No. 140508/1983.
In, for example, Japanese Patent Laid-Open No. 140508/1983, a nozzle assembly is provided which includes a tapering face formed in an inner bottom portion of the nozzle main body or nozzle chip having an orifice. A valve guiding member, having a valve guiding hole, is inserted into the nozzle main body with one end of the valve guiding member contacting the tapering face of the nozzle main body. A holding member is inserted into the main nozzle so as to fix the valve guiding member in position. By virtue of the contact between the outer diameter of the valve guiding member and tapering inner bottom portion of the main body a concentric positioning between the inner bottom portion of the main body and the valve guiding hole is achieved.
In U.K. 2,198,589, an electro-magnetic fuel injector apparatus is proposed wherein two components are combined together utilizing a metal plastic deformation. In this proposed construction, a core and a yoke are concentrically disposed in a jig, and the core and yoke are joined through plastic deformation.
The utilization of metal plastic deformation for a fuel injector apparatus is also proposed in, for example, 20 Japanese Patent Laid-Open No. 111280/1988.
A disadvantage of the above discussed conventional techniques resides in the fact that, upon inserting the holding member, the inner cylindrical component is subjected to a rotational force due to contact between the holding member and the inner cylindrical component. By virtue of the imparting of the rotational force, an accurate concentric positioning is difficult to achieve.
By virtue of the difficulty achieving positioning accuracy, even when the movable valve body contacts the valve set in a valve closing state, a clearance may exist between the movable valve body and the valve seat resulting in leakage.
Further, during a valve opening, an imbalance results causing a circular clearance between the movable valve body and the valve seat, with such circular clearance resulting in an uneven fuel spray. Further, the reciprocating movement of the control rod of the movable valve guided by the valve guiding member cannot be carried out smoothly, and an abnormal abrasion of the control rod results thereby reducing the service life of the injector. Moreover, even when the holding member is threaded into the outer cylindrical component, fine ferrite powder may occur in the threaded portion, with the fine ferrite powder adhering to, for example, the valve seat or other components of the nozzle. The presence of ferrite powder between the valve seat and the movable valve body may result in leakage of the nozzle.
In the arrangement of U.K. 2,198,589, the core and the yoke are formed as open cylindrical members and the core is inserted into the yoke, with a positioning guide being passed from a side of the yoke as the outer side of the cylinder to a side of the core as the inner side cylinder, and then a punch is operated from the opposite position in a direction opposite an insertion direction of the positioning guide.
The arrangement of U.K. 2,198,589 is difficult to apply when the outer cylindrical component has a bottom portion since, when the inner cylindrical component is fitted to the outer cylindrical component having the bottom portion, by virtue of the existence of the bottom portion, it is difficult to insert a positioning guide pin into the inner cylindrical component from the side of the outer cylindrical component.
To accommodate the positioning pin, it has been proposed to provide a hole such as an orifice in the bottom portion of the outer cylindrical component, with a hole diameter of the outer cylindrical component being smaller than a hole diameter of the inner cylindrical component; however, this proposal does not ensure positional accuracy of the component of the injector.